Controlled source electromagnetic geophysical surveys, including Induced Polarization methods (frequency, time-domain and spectral), Complex Resistivity and Controlled Source Audiomagnetotellurics (CSAMT) use electrode stations usually consisting of metal stakes or conduit driven into the earth. As shown in FIGS. 1 and 3, an electrode station 100 may consist of multiple stakes, pieces of conduit, or metallic sheets connected together with wire. Insulated wire 102 is then run on the ground from each electrode station 100 to the transmitter 101. Poor wire insulation and splices, especially when the ground is wet, can cause unwanted conduction paths to ground, creating a safety issue and potentially causing problems with accurate data collection.
Referring to FIGS. 2 and 4, time domain electromagnetic methods, as well as controlled-source audio-frequency magnetotellurics use a wire loop(s) 103 to induce a magnetic field into the ground. More than one loop of wire may be used. As with dipole-dipole methods, poor wire insulation and splices 104, especially when the ground is wet, can cause unwanted conduction paths to ground, creating a safety issue and potentially causing problems with accurate data collection.
During operation, as shown in FIGS. 1-4, the voltage at the output is switched at different frequencies and duty cycles. The transmitter is able to monitor the output current. If the current is below some set point, then the transmitter output is disabled. This method is good at detecting high resistance electrodes 100, open loops 104 (e.g., broken wires), but it is not effective at detecting current following a different path to ground. Current may flow from a splice on the wire to ground or from poorly insulated wire to ground 107. Alternatively, current may flow through a person 108 or animal if they pick up or chew on the wire. These conditions are not detected by open circuit tests and other methods currently known in the art.